It is known that fluorine can be exchanged for chlorine, bromine or iodine bonded to phosphorus by reaction of the halophosphorus compound with a metal fluoride. The transhalogenation reaction is quite slow and difficult to push to completion. It is sometimes desirable to replace chlorine, bromine, or iodine bonded to phosphorus with a fluorine atom. For example, L. P. J. Burton U.S. Ser. No. 020,023 filed Feb. 27, 1987 describes a family of hydrocarbyl fluorophosphites that are very effective stabilizers in polyolefins, especially in combination with phenolic antioxidants, and are also hydrolytically stable. These compounds are made by first forming a hydrocarbyl chlorophosphite by reaction of an appropriate aliphatic or aromatic hydroxy compound with PCl.sub.3 to form a mono or dichlorophosphite and then transhalogenating the chlorine atom with fluorine by reaction with a metal fluoride such as potassium fluoride.
L. P. J. Burton and M. S. Ao, in U.S. Ser. No. 110,198 filed Oct. 19, 1987, disclose that the transhalogenation of a chlorine, bromine or iodine atom bonded directly to phosphorus by reaction with a fluoride salt can be sharply promoted by including in the reaction mixture a hydrogen halide salt of a pyridine-type compound. While this constitutes an important contribution to the art by decreasing the amount of time required to complete the transhalogenation reaction, a disadvantage of this method is that it employs the use of expensive metal fluoride reactants, such as potassium fluoride.